desi-ms in food contaminants control

DESI-MS in food contaminants control

Michel Nielen, Hans Mol

Outline

Introduction

Principle

Experimental parameters

Instrumentation

Food contaminant applications

Summary/outlook

DESI-MS

Science 306, 471 (2004)

Desorption electrospray ionizationFirst ambient MS technique invented by Graham Cooks from Purdue University, USA

Mass spectrometry

Ambient MS techniques

Venter, Nefliu, Cooks, Trends in Anal. Chem. 27 (2008) 284-290

Ambient MSWeston, Analyst, 2010, 135, 661Weston, Analyst, 2010, 135, 661Weston, Analyst, 2010, 135, 661Weston, Analyst, 2010, 135, 661----668668668668

DESI: principle and processes

Ifaet

al,

Anal

yst,

2010

, 135

, 669

–681

From surface deposit to ion:

1. Formation of charged primary droplets by electrospray source2. Flight of droplets to surface, wetting of surface, dissolvation3. Collision of charged droplets with surface => smaller droplets4. Takeoff of secondary droplets, ablated material, free ions5. Transport through atm. pressure interface6. Shrinking of droplets, electrostatic fission => free ions

Formation of secondary droplets

Costa, Cooks, Chemical Physics Letters 464 (2008) 1–8

Experimental parameters

Venter et al, Anal. Chem. 2006, 78, 8549-8555

- Solvent- Solvent flow- Gas flow- Spray angle- Capillary voltage- Distance to sample surface- Angle ion collection MS- Sample surface- Distance to MS inlet- MS parameters (incl. source temp)

Solvent and spray

Dissolution of analyte in microdroplets / solvent film

Ionization; similar to LC-ESI-MS solvents⇒ MeOH or ACN with water/acid

Option to add reagents (reactive DESI)

Flow rate: 1-5 µl/min

Nebulizer gas: 8-40 L nitrogen/min

Spray droplets: ≤ 10 µm (2-4), v ≥ 100 m/s (120)

Reactive DESI

Ifa et al, Analyst, 2010, 135, 669–681

Spray voltage (kV)

Higher V => more charges on droplet surface

Levels off around 5 kV (=> default)

Nebulizer gas pressure (psi)

Solvent flow rate µl/min

Venter et al, Anal. Chem. 2006, 78, 8549-8555

Geometry

α = 25-80°β = ~5-10°Spray tip to surface= 1-10 mmSurface to MS inlet = 1-5 mm

Standard configuration DESI sources

Venter et al, Anal. Chem. 2007, 79, 6398

Alternative configurations

Green et al, Anal. Chem. 2009, 81, 2286-2293

Geometry independent configurations

Sample surface (substrate)

Surfaces:

Sample itself

Wettability: solvent formation/dissolutionElectroconductivity: more charge maintained by substrate,

more charge in sec. droplets

Pear leaf

Substrates for liquids/extracts:- Glass- PTFE (teflon)- PMMA (polymethylmethacrylate)- Filter paper- TLC plates

2.5 mm

5 mm

DESI, instrumentation

Paracetamol

In principle…….you can misuse a Z-source….


Ion source assembly Mass spectrometer

OmniSpray ion source

DESI, instrumentationTop view DESI source assembly

OmniSpray ion source (Prosolia)

DESI-MS/MS (LXQ, linear ion trap)

Nub

uliz

erga

s (N

2)

Pote

ntia

l (V)

Solvent

camera

light

MS inlet

sample


motorized sample stage

DESI, MS inlet (sniffers)

Extended, bended

Standard LXQ MS inlet capillary

Extended, bended,enlarged opening

Front view DESIZ

X

Y

X

Y

Z

Spray head

Y Z

X

DESI applicationsDESI and related ESI approaches by far most utilized ambient MS technique*

Rapid analysis pharmaceutical productExplosivesBiological imagingForensic imaging of inksIllegal and counterfeit drugsDrug metabolites in biological matricesChemical warfare agentsTextilesPeptides and proteinsProteomicsMetabolomicsPlants / natural productsFood contaminants…….

*Weston, Analyst 135 (2010) 661-668

Test MRL compliance: Homogenisation (+extraction) => deposit on spots/slides(semi) Quantitative analysis

DESI in food contaminants control

Consideration MRL verification ⇒ MRLs expressed in mg/kg whole product⇒ requirements minimum sample size

In laboratoryDESI for fast

high throughput analysis of extracts

In laboratoryFast high throughput analysis of sampleDistribution on surface/cross sections

In-field DESI as on-site detection tool

Food forensicscrops, swops, clothing, containers, syringes

Test presence (screening, yes/no)Direct detection from sample surfaceor cross-sections of tissuesNo sample preparationQualitative

Feasibility Dithiocarbamates by DESIFungicides, widely used, high application ratesNon-systemic (residues on surface only)

PBDC = propylenebis(dithiocarbamate)

DMDC = bis(dimethyldithiocarbamate)

thiram zirampropineb

maneb

EBDC = ethylenebis(dithiocarbamate)

Groups and examples of individual products to which the MRLs apply (a)

Dithiocarbamates (dithiocarbamates expressed as CS2, including maneb, mancozeb, metiram, propineb, thiram

and ziram)

Propineb (expressed as

propilendiamine)

Thiram (expressed as

thiram) Ziram

Apples 5 0,3 5 0,1*Pears 5 0,3 5 1Strawberries 10 (ft) 0,05* 10 0,1*Lettuce 5 0,05* 2 0,1*

Solubility issues

Stability issues

Current method: hydrolysis to CS2

Legislation (396/2005): CS2 (sum) but specific MRL for 3 DTCs

Dithiocarbamates

……..+ 10 mM NH4CH3COO

081114_01 #56 RT: 0.54 AV: 1 NL: 3.20E1T: ITMS + p ESI Full ms [100.00-500.00]

100 150 200 250 300m/z

0

10

20

30

40

50

60

70

80

90

100

Rel

ativ

e A

bund

ance

263.0

273.3

295.1261.3

238.8 293.2229.3

217.2 246.9120.0 193.2183.3

208.9130.2152.8

081114_02 #8-22 RT: 0.07-0.21 AV: 15 NL: 6.40T: ITMS + p ESI Full ms [100.00-500.00]

100 150 200 250 300m/z

0

10

20

30

40

50

60

70

80

90

100

Rel

ativ

e A

bund

ance

217.2

120.0 241.0

149.1

228.3

287.0267.1

244.1251.2

195.3152.0193.2

130.2

MS: 263 [M+Na](MS/MS weak 143) MS: 241 [M+H]

MeOH/water 1:1 , 0.1% FA

MS/MS optimization (thiram)

081114_08 #22-76 RT: 0.28-0.99 AV: 55 SB: 31 1.10-1.50 NL: 8.01T: ITMS + p ESI Full ms2 [email protected] [65.00-300.00]

100 150 200 250 300m/z

0

10

20

30

40

50

60

70

80

90

100

Rel

ativ

e A

bund

ance

195.9

88.1

120.0 172.9 223.0139.072.0 235.0

Product ion spectrum

DESI parametersNitrogen sheath gas Incident angleSpray tip-to-surface distanceSurface to MS-inlet distanceScattering angle DESI spray

FlowScanning of the surfaceHeated capillary MS (LXQ)Substrate

120 psi (9 bar)55o

5 mm1 mmca. 10o to surfaceMeOH/water 1:1+ 10 mM NH4For. + 0.1% FA5 µl/min250 µm/sec50oCPTFE printed on glass

Thiram stnd solutions (teflon spots on glass)

RT: 0.00 - 2.10 SM: 3G

0.0 0.5 1.0 1.5 2.0Time (min)

0

20

40

60

80

100

0

20

40

60

80

100

RT: 1.38MA: 185 RT: 1.63

MA: 321

RT: 0.98MA: 179

RT: 0.77MA: 70.37

RT: 0.52MA: 17.19

RT: 0.18MA: 0.00

1.52

1.121.26

2.020.56 1.94

RT: 1.03MA: 3586

RT: 0.51MA: 3888 RT: 0.76

MA: 4079RT: 0.28MA: 3581 RT: 1.50

MA: 2474RT: 1.26MA: 3095

1.65

1.060.55

2.020.05 1.81

NL: 9.07E1m/z= 195.50000-196.50000 F: ITMS + c NSI Full ms2 [email protected] [80.00-250.00] MS 100422_31


0 0.1 0.25 0.50.75 1.0

mg/LThiram

ISTDmm 307.5 22.5

Quantitative analysis?

Cal Curve Thiram 0-1 mg/kg Average n=3

y = 0.1428x - 0.0057

R2 = 0.9761

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0 0.2 0.4 0.6 0.8 1 1.2

mg/L ~ mg/kg →

Direct analysis from sample surface

Alternative to direct analysis

Homogenization (plant juices); simple extraction procedure followed by rapid DESI detection

Options extraction:

Systemic: QuEChERS or other

Non-systemic: solvent rinse of intact product

QuEChERS: 1. Initial Extraction Step

Weigh 10 g Sample

Add 10 mL MeCN

Shake Intensively

for 1 min

Slides from Anastassiades et al, (JAOAC, 2003)

2. Extraction/Partitioning Step

(Pre-)Weigh 4 g MgSO4 + 1 g NaCl

Add to the Tube

Shake Intensively

for 1 min


3. Addition of ISTD and Centrifugation

Add ISTD

Shake for 30 s

Centrifuge (ca. 5 min)

Separated Raw Extract


4. Dispersive SPE Step

(Pre-) Weigh MgSO4 and PSA

Add Extract to Tube and Shake ca. 30 s

Centrifuge (ca. 2 min)

Cleaned up Extract


Surface extraction

RT: 0.00 - 1.90 SM: 5G

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8Time (min)

0

20

40

60

80

1000

20

40

60

80

1000.28

0.370.57

0.62

1.13

1.03

0.781.36

1.56 1.840.080.30

0.580.34

0.79

1.34

1.08 1.110.86 1.39 1.851.511.26

0.07



x15

Comparison of extraction methods (pear)solvent

Surface extract

QuEChERSThiram

ISTD

w/o buffer acetate buffer

no dSPE w dSPE

Spike experimentsVegetables/fruits spiked with thiram std and commercial PPP (TMTD)

1.5 µl strawberry extracts Ref. std thiram

RT: 0.00 - 2.10 SM: 7G

0.0 0.5 1.0 1.5 2.0Time (min)

0

20

40

60

80

1000

20

40

60

80

1001.53

1.320.78

0.871.63

1.07 2.020.60 1.790.400.130.63

1.54

0.84 1.33

1.06 1.610.540.28 2.021.790.08



Control Control Control Control

Spiked Spiked Spiked Spiked ThiramThiramThiramThiram

Spiked Spiked Spiked Spiked TMTDTMTDTMTDTMTD

Strawberry MRL level

ISTD ISTD ISTD ISTD

Results

100422_20 #61 RT: 0.38 AV: 1 NL: 8.60E3F: ITMS + c NSI Full ms2 [email protected] [80.00-250.00]

80 100 120 140 160 180 200 220 240m/z

0

20

40

60

80

100

Rel

ativ

e A

bun

dan

ce

195.9

87.9120.0 223.0151.9 183.1 209.0188.2 197.0167.0131.4112.8 140.097.185.1

DaughterscanDaughterscanDaughterscanDaughterscan m/z 241 @ CE25 Solvent Standardm/z 241 @ CE25 Solvent Standardm/z 241 @ CE25 Solvent Standardm/z 241 @ CE25 Solvent Standard

100422_20 #175 RT: 1.09 AV: 1 NL: 1.28E2F: ITMS + c NSI Full ms2 [email protected] [80.00-250.00]

80 100 120 140 160 180 200 220 240m/z

0

20

40

60

80

100

Rel

ativ

e A

bun

dan

ce

196.0

223.2188.1

206.2

183.0 205.2 224.2149.3 209.287.9 163.3143.1117.3109.196.9 125.1 178.9

DaughterscanDaughterscanDaughterscanDaughterscan m/z 241 @ CE25 Strawberry spikedm/z 241 @ CE25 Strawberry spikedm/z 241 @ CE25 Strawberry spikedm/z 241 @ CE25 Strawberry spiked

Results

thiram ISTD ratio1 3333 5568 0.602 9398 7561 1.243 6124 5759 1.064 6552 6623 0.995 3414 5054 0.686 5117 5490 0.93

average 5656 6009 0.92RSD% 40 15 26av. Rec.% 85

Results

Recovery and repeatability (matrix-matched calibration)

Pears spiked (10 mg/kg)

Strobilurin fungicides (Biocop)

BioCopSchurek et al, Anal. Chem. 80 (2008) 9567-9575

Azoxystrobin MS/MS on m/z 404

071102_hho__20 #239 RT: 7.13 AV: 1 NL: 1.14F: ITMS + p ESI Full ms3 [email protected] [email protected] [100.00-1250.00]

120 140 160 180 200 220 240 260 280 300 320 340 360 380 400m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nda

nce

344.08

316.08

303.00

287.00172.00

326.08

272.08244.00201.00144.83 216.00134.00 184.92160.92 260.92 357.33

071109_hho__13 #13-24 RT: 0.34-0.66 AV: 12 NL: 2.51E1F: ITMS + p ESI Full ms3 [email protected] [email protected] [100.00-500.00]

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nda

nce

344.08

316.08

303.00

287.08171.92

329.00201.00 274.08210.00134.00 145.00 260.17196.92 354.25229.00 372.25115.83

Standard 20 ng/spot Ziptip extraction

strobilurin DESI from PTFE Reactive DESI silver cationization

Metominostrobin "Z" + + Metominostrobin "E" + + Fenamidone + +/- Kresoxim-methyl - + Dimoxystrobin +/- + Epoxiconazole + +/- Famoxadone - +/- Pyraclostrobin - + Orysastrobin - + Azoxystrobin + + Trifloxystrobin - + Fluacrypyrim - + Fluoxastrobin + + Picoxystrobin + +

Strobilurins: Reactive DESI

DESI: ACN/water/FA (80:20:0.1)reactive DESI: ACN/water (75:25) + 5 mg/ml AgCF3COOH flow 2.5 ul.min-1

Pesticides in/on vegetables/fruits

Garía-Reyes et al, Anal. Chem. 81 (2009) 820-829

Optimization of spray solvent

DESI parameters garcia et al

Nitrogen sheath gas Incident angleSpray tip-to-surface distanceSurface to MS-inlet distanceScattering angle DESI spray FlowScanning of the surfaceHeated capillary MS (LTQ)Substrate

150 psi (10 bar)55o

5 mm1.5 mmca. 10o to surfaceacetonitrile/water 8:2+1% FA5 µl/min?200oCPTFE

Garía-Reyes et al, Anal. Chem. 81 (2009) 820-829

QuEChERS w/o buffer + PSA clean up; extract diluted 1:3 in acetonitrile


Direct detection of imazalil from lemon peel

Full scan spectrum of peel

MS/MS spectrum standard

MS/MS spectrum m/z 297 peel

MS/MS spectrum m/z 299 peel



using deuterated imazalil as ISTD

Reactive DESI analysis on steroidsSteroids in urineSPME enrichmentDirect detection from fiber

Spray 3µl/min:MeOH/water 1/1 0.05% HAc, 5% hydroxylamine

Huang et al, Anal. Chem. 79 (2007) 8327-8332

Steroid cocktailO:\D ata_ D ESIMS\...\0 70 91 2\0 70 91 2_ hh o __ 40 9/1 2/20 07 12 :4 5 :5 8 PM rik 1 67 46 92 .5 µ l/m in MeOH /0 .2 % FA 1 /1 in j. vo l.: 0 .0 0 00 00

07 09 12 _h h o_ _4 0 #3 1 R T: 0 .08 AV: 1 N L : 5 .1 4E3T: ITMS + c ESI Fu ll m s [50 .0 0 -1 2 50 .0 0]

27 0 28 0 2 90 30 0 3 10 32 0 3 30 34 0 35 0 3 60 37 0 3 80 3 9 0 4 00 4 1 0 42 0 4 30 44 0 4 50 4 6 0m /z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

10 0

Re

lativ

e A

bu

nd

an

ce

3 11 .52

3 87 .3 3

31 5.55

4 13 .4 830 3.6 028 5.64

32 8.3 72 83 .5 7 3 01 .5 9

3 37 .4 532 5.34

2 97 .6 44 43 .463 8 8.49

3 29 .4 23 09 .5 7 4 1 4.5231 6 .5 136 5.39

27 1.6 7 44 4.5 033 8.5728 6 .6 5 3 17 .47 3 3 1.36 3 73 .3 035 7.4 0 39 1.3 92 7 9.57 34 5.28 40 3.42 4 22 .4 3 44 5.3 3 4 57 .4 93 81 .4 2 4 31 .1 52 95 .57

MeBol

ChlT�Ac

MeT/Noreth Fluoxy

Prog

MP�Ac

T�cyp

T�phep

T�deca

0 7 0 9 12 _ h h o __ 4 0 # 53 RT : 0 .14 A V: 1 NL : 1 .2 6 E3F: IT M S + c ES I d Fu l l m s2 3 0 1.6 4 @cid 3 5 .0 0 [7 0 .0 0 -6 1 5 .0 0 ]

1 00 1 5 0 2 0 0 2 50 3 0 0

m /z

0

5

1 0

1 5

2 0

2 5

3 0

3 5

4 0

4 5

5 0

5 5

6 0

6 5

7 0

7 5

8 0

8 5

9 0

9 5

1 0 0

Re

lativ

e A

bun

da

nce

2 8 3 .1 8

1 49 .0 1

2 8 4 .2 412 1 .0 2 17 3 .0 2

1 6 3 .0 4 1 8 7 .1 1 2 0 1 .0 52 27 .1 4 2 5 5 .051 0 6 .9 89 3.0 2 2 9 3 .3 3 3 19 .9 7

070912_hho__40 #2-35 RT: 0.03-0.08 AV: 3 NL: 2.81E2F: ITMS + c ESI d Full ms2 [email protected] [80.00-685.00]

100 120 140 160 180 200 220 240 260 280 300 320 340m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bun

da

nce

281.18

299.19

317.20

263.23241.09

223.10

239.16319.23

257.24225.06207.13

291.23237.17159.16 301.22173.05 221.15145.08 185.13

199.02131.00171.13 273.14 305.20121.02 229.18195.10 243.14142.96109.06

322.55 333.21309.16102.93

Steroid cocktailMethylboldenone MS/MS m/z 301 Fluoxymesterone MS/MS on m/z 337

RT: 0.00 - 2.25 SM: 7B

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nda

nce

1.911.88

1.86

1.93

1.96

1.79

1.151.13

1.11

1.201.08

1.22

1.03

2.190.80 1.461.01 1.39 1.48

NL:9.98

TIC MS 081010_081010140847

RIC MS2

360>316

DESI conditions

MeOH/H2O/FA (50:50:0.1) at 1.5 µl/min

Angles: impact 60°, collection 10°

Distances: ESI-chip 3 mm; chip-inlet 6 mm

X-position scanrate 170 µm/s; # tracks: 3

Nitrogen 120 psi

#1

#2

RT: 0.00 - 2.25 SM: 7B

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nda

nce

1.911.88

1.86

1.93

1.96

1.79

1.151.13

1.11

1.201.08

1.22

1.03

2.190.80 1.461.01 1.39 1.48

NL:9.98

TIC MS 081010_081010140847

RIC MS2

360>316

DESI conditions

MeOH/H2O/FA (50:50:0.1) at 1.5 µl/min

Angles: impact 60°, collection 10°

Distances: ESI-chip 3 mm; chip-inlet 6 mm

X-position scanrate 170 µm/s; # tracks: 3

Nitrogen 120 psi

#1

#2

081010_081010140847 #8-126 RT: 0.85-2.22 AV: 59 NL: 3.07E-1F: ITMS + c ESI Full ms3 [email protected] [email protected] [85.00-400.00]

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bund

anc

e

245.12

285.06204.06

268.36231.37 315.93

245

360

316

081010_081010140847 #82-118 RT: 1.71-2.13 AV: 19 NL: 3.35F: ITMS + c ESI Full ms2 [email protected] [95.00-400.00]

100 120 140 160 180 200 220 240 260 280 300 320 340

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nd

an

ce

316.21

342.09

340.19314.01

302.54 344.25161.06 325.39292.09279.34238.73 267.23116.86 173.84 209.03

316

342

360

081010_081010140847 #8-126 RT: 0.85-2.22 AV: 59 NL: 3.07E-1F: ITMS + c ESI Full ms3 [email protected] [email protected] [85.00-400.00]

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bund

anc

e

245.12

285.06204.06

268.36231.37 315.93

245

360

316


100 120 140 160 180 200 220 240 260 280 300 320 340

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nd

an

ce

316.21

342.09

340.19314.01

302.54 344.25161.06 325.39292.09279.34238.73 267.23116.86 173.84 209.03

316

342

360

245

360

316

360

316


100 120 140 160 180 200 220 240 260 280 300 320 340

m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nd

an

ce

316.21

342.09

340.19314.01

302.54 344.25161.06 325.39292.09279.34238.73 267.23116.86 173.84 209.03

316

342

360

Direct detection of IA captured fluoroquinolone

SPR biosensor chipImmunoaffinity bound enrofloxacin

Nielen et al, Poster ISMS, Bremen, 2009

Alkaloids on Senecio jacobaea L. Stinking Willie

O

O

HO CH3

H3C

O

N

HO

CH2

+

O-

O

O

HO CH3

H3C

O

N

HO

CH2

Reduction

Senecionine N�oxide Senecionine

Unable to passively permeate membranes

Nontoxic

Metabolically safe

Able to passively permeate membranes

Toxic after bioactivation

Metabolically unsafe

071003_hho__29 #16 RT: 0.38 AV: 1 NL: 6.49E2T: ITMS + c ESI Full ms2 [email protected] [95.00-450.00]

100 150 200 250 300 350m/z

0

10

20

30

40

50

60

70

80

90

100

Rel

ativ

e A

bund

ance

308.14

280.10

262.18

154.98120.03 282.29234.11200.11 324.24162.06 306.11244.11146.05 190.19 335.04 353.69

Senecionine

MS/MS spectrum m/z 352

Alkaloids on Senecio jacobaea L. Stinking Willie

SummaryDESI a useful option for food contaminant analysis/controlLots of research in progress, many papers appearingLike other ambient techniques, pro’s and con’s

Features: - Direct detection from substrates, TLC, sensor chips, sample surface- Reactive DESI- Spatial resolution- Rapid detection/high throughput of sample(extracts)Quantitative determination possible with use of internal standard

Limitations:- Sensitivity (matrix suppression)- Reproducibility- MSn or high res required - residues => targeted detection

OutlookIn lab analysis:- Further improvement robustness- Rapid straightforward and selective extraction- More applications- Combi sources to extent scope

ASAP+DESI (Lloyd et al, Anal. Chem. 81, 2009, 9158)

Towards in-field:- optimization of nongeometry dependent DESI source- coupling of DESI with portable MS instruments- …..

Too much, too little, too fast, not clear?

Submitted to Trends in Analytical Chemistry (March 2010)

DESI, spray video

Venter, Nefliu, Cooks, Trends in Anal. Chem. 27 (2008) 284-290

DESI spray on surface video clip.wmv

DESI, Alternative geometries

Ifa et al, Analyst 135 (2010) 669-681

desi-ms in food contaminants control

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